Radioactive characterization of gas-solid flows in a conical spouted bed

info:eu-repo/semantics/nonPublishe

Radioactive characterization of the gas residence time distribution in spouted beds

info:eu-repo/semantics/nonPublishe

Evaporation versus imbibition in a porous medium

Predicting and controlling the liquid dynamics in a porous medium is of large importance in numerous technological and industrial situations. We derive here a general analytical solution for the dynamics of a flat liquid front in a porous medium, considering the combined effects of capillary imbibition, gravity and evaporation. We highlight that the dynamics of the liquid front in the porous medium is controlled by two dimensionless numbers: a gravity–capillary number G and an evaporation–capillary number E. We analyze comprehensively the dynamics of the liquid front as functions of G and E, and show that the liquid front can exhibit seven kinds of dynamics classified in three types of behaviors. For each limiting case, a simplified expression of the general solution is also derived. Finally, estimations of G and E are computed to evidence the most common regimes and corresponding liquid front dynamics encountered in usual applied conditions. This is realized by investigating the influence of the liquid and porous medium properties, as well as of the atmospheric conditions, on the values of the dimensionless numbers.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Convective drying of fermented Amazonian cocoa beans (Theobroma cacao var. Forasteiro). Experiments and mathematical modeling

The general objective of this work is to contribute to the characterization and the mathematical modeling of the convective drying of fermented Amazonian cocoa beans (Theobroma cacao var. Forasteiro). A combined approach is used, including the analysis of the bean physical characteristics, the determination of the bean sorption isotherms, the realization of drying experiments in a convective dryer (for different operating conditions) and the development of a mathematical model, based on the different transport (heat and mass) phenomena involved inside and outside the beans during their drying. The results show that the drying of an Amazonian cocoa bean can be divided in two phases. It is demonstrated that this is due to the combination of two elements. First, the initial volumetric concentration of water is higher in the shell than in the core of the bean. Second, at the beginning of the drying, the drying rate is controlled by both internal and external transport phenomena while, in the second part of the drying (for moisture content of the bean below 0.5 kg of water/kg of dry matter), it is totally controlled by the water diffusion inside the bean. The model is compared to the experimental results in order to characterize the effective diffusion coefficient of water inside a bean. It is shown that this diffusion coefficient approximately doubles when the temperature is increased from 30 to 60 °C. It is close to 1.5 × 10−10 m2/s at 60 °C. Finally, measuring the polyphenol content of the dry beans allows assessing that, regarding chocolate quality, the fermented Amazonian cocoa beans should be dried at 30–40 °C.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Convective drying of baker’s yeast pellets containing a carrier

The drying behavior of yeast pellets containing a carrier was investigated. Yeast paste was mixed with different amounts of wheat flour, a solid carrier, to obtain spherical pellets with 69, 55, and 40 wt% of water. During the drying, the pellets moisture content, surface temperature, and dimensions were measured, using a balance, an infrared camera, and a stereomicroscope, respectively. A drying kinetics model was developed and successfully challenged to the experimental results. The experimental and modeling results give insights into the phenomena taking place during the drying of yeast pellets including a carrier. These results highlight that the addition of a carrier reduces the shrinkage of the pellets and increases the drying rate. Moreover, the results seem to indicate that an osmosis process may take place inside the pellets following the addition of the carrier.SCOPUS: ar.jinfo:eu-repo/semantics/publishe